Black Screen With a Flashing White Line - any Ideas

[siam]

I have an iMac 2.8 24 inch, about Two years old running 10.5.7 , when I start the computer it shows the normal Gray screen
for about 30 seconds, then the screen goes all Black , but with a small flashing white line ( _ ) in the top Left hand side corner.

It just stays all Black for ever , I then hold down the On / Off button and turn off the computer, I then hold down the keyboard
'' option key '' and press the on button at the same time , then I get the option to start from the main HDD , I click the Icon and the computer then starts normally , and every thing runs ok.

Can some one please tell me what I have to do to get my iMac to start up normally again , Ive run Repair Disk permissions but the problem still occurs . Over the last few day's Ive been trying out a few new applications, so not too sure if this has any thing to do with this current problem


Thanks

[yoyo5280]

Go in system preferences and check what your startup disk is real fast...

-Omi

[killerrobot]

Looks like your startup disk has been changed.

Go to >system preferences>startup disk

Make sure you have the Disk that shows 10.5.8 installed on it.

EDIT: Yeah! What yoyo said.

[siam]

Thanks guy's , it was starting up from one of the applications I was trying out
and not the main HDD

Many Thanks